"Structural and functional divergence within the Dim1/KsgA family of rRNA methyltransferases."

The enzymes of the KsgA/Dim1 family are universally distributed throughout all
phylogeny; however, structural and functional differences are known to exist. The
well-characterized function of these enzymes is to dimethylate two adjacent
adenosines of the small ribosomal subunit in the normal course of ribosome
maturation, and the structures of KsgA from Escherichia coli and Dim1 from Homo
sapiens and Plasmodium falciparum have been determined. To this point, no
examples of archaeal structures have been reported. Here, we report the structure
of Dim1 from the thermophilic archaeon Methanocaldococcus jannaschii. While it
shares obvious similarities with the bacterial and eukaryotic orthologs, notable
structural differences exist among the three members, particularly in the
C-terminal domain. Previous work showed that eukaryotic and archaeal Dim1 were
able to robustly complement for KsgA in E. coli. Here, we repeated similar
experiments to test for complementarity of archaeal Dim1 and bacterial KsgA in
Saccharomyces cerevisiae. However, neither the bacterial nor the archaeal
ortholog could complement for the eukaryotic Dim1. This might be related to the
secondary, non-methyltransferase function that Dim1 is known to play in
eukaryotic ribosomal maturation. To further delineate regions of the eukaryotic
Dim1 critical to its function, we created and tested KsgA/Dim1 chimeras. Of the
chimeras, only one constructed with the N-terminal domain from eukaryotic Dim1
and the C-terminal domain from archaeal Dim1 was able to complement, suggesting
that eukaryotic-specific Dim1 function resides in the N-terminal domain also,
where few structural differences are observed between members of the KsgA/Dim1
family. Future work is required to identify those determinants directly
responsible for Dim1 function in ribosome biogenesis. Finally, we have
conclusively established that none of the methyl groups are critically important
to growth in yeast under standard conditions at a variety of temperatures.

This publication refers to following proteins:

RsmA (Saccharomyces cerevisiae)

RsmA (Methanocaldococcus jannaschii)

Entry added on: 2011-10-15 17:29:41.295852, by a user: magda

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